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Chemistry notes A-C & Chpt 1.docx

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Chemistry 1027A/B
Kay Calvin

CHEMISTRY 1100A~ NOTES A-D and CHPT 1. Topic A:atoms,Molecules and Moles A.1 Atoms -building blocks of all elements -3 componente :proton neutron and electron -protons-+ve -neutrons-neutral -electrons- -ve proton n neutrons-found in nucleus of atom -electrons occupy space around the nucleus Protons n neutrons-have same mass. & make up most of the atom -electrons small n light-1/200th of mass of a proton or neutron Atomic Number -all atoms of the same element have same # of protons in the nucleus ex-6 protons=C # protons in a atom =atomic #. Atomic # of C=6 b/c 6 protons Mass Number mass #= total # protons +# neutrons in an atom MASS #=NUMBER OF PROTONS+NUMBER OF NEUTRONS Notation azX ^mass # & atomic number of element A-mass number Z-atomic # , X-chemical symbol for element -another notation chemical symbol followed by mass number ex- Na-23 ISOTOPES -same # of protons but different # of neutrons=isotope -same atomic #,diff mass # ex-C-12=(6p+6n) C-14=(6p+8n) -some elements have more then 1 isotope and there can be more then 1 isotope than another ( 1 isotope can be more commonly found then another) -isotopic abundance is the % by # of each of the isotopes of an element. ISOTOPIC ABUNDANCE AND AVERAGE ATOMIC MASS -atomic mass assigned to each element is the average value of the masses of all of the isotopes of that element ex- since most silicon in the world is SI-28 the average atomic mass is closer to 28u rather than its other isotopes AVERAGE ATOMIC MASS= PERCENT ISOTOPIC ABUNDANCE/100 X ISOTOPIC MASS ATOMIC MASS STANDARD -atomic mass standard is based on the mass of C-12. -atomic masses of all other elements in the periodic table have been measured using C- 12 -1 AMU is define as exactly 1/12 the mass of C-12 IONS -All neutral atoms have an equal # of protons & electrons -the atomic number Z is also # of electrons in neutral atom atom loses electron +ve charge = to the # of electrons lost. ex-Li 2+ ( lost 2 e- ) ^ CATION (cat has paws) atom gains electron = -ve charge ex-Li- (gained 1) ^ANION -term ion is used for atoms that have gained or lost electrons A.2 MOLECULES AND COMPLEX IONS -molecules are atoms bonded together in a specific ratio-ex HNO3 -compound-molecule containing more then one element -complex ion-are ions of molecules diatomic-only to atoms ex-O2 polyatomic-more than 2 atoms -# of atoms present in a molecule is determine by electronic consideration THE MOLE AND AVOGADROS NUMBER -impsoible to work with small # of molecules --chemical experimentation-amount of species is expressed in moles -one mole is the number of atoms exactly in 12 grams of C-12 Avogadros #-6.023x10^23 moles=n -1 mole of anything is 6.02x10^23-used for atoms molecules and ions USING AVAGADROS NUMBER -determine # of individual atoms ,molecules or ions in a sample -number of moles of atoms x Na=number of atoms to find the number of atoms in a sample of molecules or ions: number of moles of molecule or ions x na-# molecules or ions number of molecules or ions x number of atoms per molecule=total number of atoms. A.3 MASS,MOLECULAR MASS AND MOLAR MASS mass of one molecule is the sum of the masses of all the atoms in the molecule=molecular mass periodic table-average mass of one atom in atomic mass unit-amu -mass of one mole of molecules =molar mass & is the sum of the masses of all the atoms used in the molecule n=m/M MASS PERCENT Mass percent=mass of one species/total mass of sample x100 -value of mass % will always be less than 100% -sum of mass % for all species involved =100% mass % can be used to find empirical formula-have mass but need mole ratios empirical formula- simplest ration of the atoms in the molecule -molar mass of the molecular formula-determine the # of empirical units in the molecular formula -if the molar mass of the of the empirical formula is the same as molar mass of the compound .-molecular formula=emprical formula MOLE FRACTION AND MOLE PERCENT mole fraction=# of moles of one species/total of moles
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